CN115246718A - Special shrinkage regulation anti-cracking agent for ultra-high performance concrete - Google Patents
Special shrinkage regulation anti-cracking agent for ultra-high performance concrete Download PDFInfo
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- CN115246718A CN115246718A CN202210825016.0A CN202210825016A CN115246718A CN 115246718 A CN115246718 A CN 115246718A CN 202210825016 A CN202210825016 A CN 202210825016A CN 115246718 A CN115246718 A CN 115246718A
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
- C04B40/0028—Aspects relating to the mixing step of the mortar preparation
- C04B40/0039—Premixtures of ingredients
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
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Abstract
The invention provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, belonging to the technical field of building material additives. The special shrinkage regulation anti-cracking agent comprises the following raw materials in parts by weight: 50-70 parts of light-burned magnesium oxide; 20-35 parts of a hydration heat absorbent; 5-20 parts of super absorbent resin; the hydration heat absorbent is prepared by slowly dripping prepolymer into paraffin emulsion, heating to 60-80 ℃ and reacting for 2-4 h; after the reaction is finished, taking out a sample, and washing and filtering the sample to obtain the product; the prepolymer is prepared from melamine and formaldehyde. The prepared special shrinkage regulation anti-cracking agent for the ultra-high performance concrete can effectively solve the self-shrinkage and drying shrinkage of the ultra-high performance concrete, improve the volume deformation and improve the durability and the later strength; when the mixing amount of the additive is 10wt% of the rubber premix, the 7d drying shrinkage value can be reduced by at least 40.4%, and the 28d drying shrinkage value can be reduced by at least 32.9%.
Description
Technical Field
The invention belongs to the technical field of building material additives, and particularly relates to a special shrinkage regulation anti-cracking agent for ultra-high performance concrete.
Background
Ultra High Performance Concrete (UHPC) is an important development direction of modern Concrete technology due to its Ultra High strength, high workability, high toughness and High durability. UHPC improves the gradation of particles, reduces internal defects and improves the compactness and uniformity of materials by removing coarse aggregates according to the close packing principle; the volcanic ash effect and the filling effect of the active mineral admixtures such as the silica fume, the fly ash and the mineral powder are utilized, so that the pore structure of the material is improved; by using the polycarboxylic acid high-efficiency water reducing agent, the water-cement ratio is greatly reduced, and the porosity is reduced, so that the concrete material with excellent performance is obtained. But the coarse aggregate is removed, so that the inhibition effect of the aggregate on the shrinkage of the basic body is reduced, and the shrinkage is larger; and because the UHPC cementing material content is high, the water-gel ratio (w/b) is low, the relative humidity in the concrete material is low due to the cementing material hydration and other factors, the water in a large number of capillary holes is changed into an unsaturated state from saturation, and the self-drying phenomenon is serious. If the early shrinkage of the concrete caused by self-drying cannot be effectively controlled, the concrete can crack due to self-stress under the constraint condition, the appearance of a building is influenced, a channel is provided for an external erosion medium to enter the concrete, the service life of the building is seriously shortened, even the bearing capacity of the concrete structure is changed, and the use safety is threatened.
Therefore, the expansion agent is mixed in the concrete to compensate the shrinkage, which is a better means for solving the shrinkage cracking problem. At present, calcium oxide, calcium sulphoaluminate, magnesium oxide and calcium oxide-calcium sulphoaluminate composite expanding agents are mainly used in the market. However, the reaction characteristics, the expansion generation time, the water demand and the expansion amount of each expanding agent are different, and the shrinkage of UHPC is greatly different from that of common concrete, wherein the UHPC mainly has self-shrinkage, the early shrinkage has high development rate and large shrinkage, and the later shrinkage is only small. Therefore, a special shrinkage regulation anti-cracking agent matched with the ultra-high performance concrete needs to be researched according to the characteristics of the ultra-high performance concrete.
Disclosure of Invention
The invention aims to provide a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which can reduce temperature-drop shrinkage generated by hydration heat and ensure that enough water is in capillary holes of the ultra-high performance concrete with low water-cement ratio to maintain continuous hydration of cement. The water in the capillary holes has the other functions of reducing the shrinkage of the ultra-high performance concrete, improving the volume deformation performance of the ultra-high performance concrete, reducing the cracking risk of the ultra-high performance concrete and improving the long-term durability of the ultra-high performance concrete.
In order to achieve the purpose, the invention adopts the following technical scheme:
the special shrinkage-regulating anti-cracking agent for the ultra-high performance concrete is characterized by comprising the following raw materials in parts by weight: 50-70 parts of light-burned magnesium oxide; 20-35 parts of a hydration heat absorbent; 5-20 parts of super absorbent resin; the preparation method of the hydration heat absorbent comprises the following steps: slowly dripping the prepolymer into the paraffin emulsion, heating to 60-80 ℃, and reacting for 2-4 h; after the reaction is finished, taking out a sample, washing and filtering to obtain a hydration heat absorbent; the mass ratio of the prepolymer to the paraffin emulsion is 1 (3-4); the prepolymer is prepared from melamine and formaldehyde.
The light-burned magnesium oxide has the advantages of low hydration water demand, stable hydration product, long expansion duration, adjustable expansion and the like, can improve the volume shrinkage problem of the ultra-high performance concrete, and reduces the shrinkage and cracking risks of the ultra-high performance concrete. The hydration heat absorbent can absorb a large amount of heat in the hydration heat release process of the concrete, so that the temperature rise inside the concrete is not too fast, on one hand, the moisture absorption heat absorbent is favorable for reducing cracks generated due to temperature stress, and on the other hand, the moisture evaporation is favorable for reducing the self-drying phenomenon caused by too low humidity inside the concrete. Super Absorbent Polymer (SAP) is a kind of novel macromolecular material that has very high water absorption rate, is an ideal interior maintenance material, through SAP absorb water in advance, when inside moisture of cement matrix material consumed, when relative humidity reduced, SAP can in time release water and moisturizing to around, guaranteed the inside relative humidity of whole material to effectively reduce its drying shrinkage and self-contraction.
Preferably, the preparation method of the prepolymer is as follows:
evenly mixing melamine, formaldehyde solution and deionized water, adjusting the pH value of the solution to 7-9 by using alkali, heating to 50-90 ℃ while stirring, and keeping the temperature for 30-80 min to obtain a prepolymer; the mass fraction of formaldehyde in the formaldehyde solution is 37-40%; the mass ratio of the melamine to the formaldehyde solution to the deionized water is 1 (1-5): (1-10).
Preferably, the mass ratio of the prepolymer to the paraffin emulsion is 1:4.
Preferably, the mass ratio of the melamine to the formaldehyde solution to the deionized water is 1.
Preferably, the base is triethanolamine.
Preferably, the preparation method of the paraffin wax emulsion comprises the following steps:
mixing styrene-maleic anhydride copolymer, sodium hydroxide and deionized water, heating to 70-90 ℃, keeping the temperature for 1-2 h, adjusting the pH value of the solution to 4-5.5 by using acid, adding paraffin, emulsifying the paraffin solution at 15500-16500 rpm after the paraffin is melted, maintaining the emulsifying temperature at 50-90 ℃, and emulsifying for 2-5min; the mass ratio of the styrene-maleic anhydride non-return copolymer to the sodium hydroxide to the deionized water to the paraffin is 1: (0.15 to 0.25): (40-50): (10 to 30).
Further preferably, the mass ratio of the styrene-maleic anhydride copolymer, sodium hydroxide, deionized water and paraffin wax is 1.
Further preferably, the acid is citric acid or/and tartaric acid.
Preferably, the light-burned magnesia is obtained by taking magnesite as a raw material, crushing, grinding, sieving with a 200-mesh sieve, and calcining at 900-1150 ℃ for 1-3 h; the content of magnesium oxide in the light-burned magnesium oxide is more than 80 percent, and the residue on a sieve with the diameter of 0.075mm is less than or equal to 10 percent.
Further preferably, the preparation method of the light calcined magnesia comprises the following specific steps:
crushing magnesite into particles smaller than or equal to 10mm in a two-section one-closed-circuit process consisting of a jaw crusher, a cone crusher and a vibrating screen, grinding the particles by a ball mill, sieving the particles by a 200-mesh sieve, entering a flotation process, adding an amine cation collecting agent and a foaming agent under the natural pH value of ore pulp, stirring the mixture at the speed of 800-1000 rpm for 40-60 min, and calcining the obtained concentrate and middlings for 1-3 h at the temperature of 900-1150 ℃ through one-rough one-fine reverse flotation to obtain light-burned magnesium oxide; the dosage of the amine cationic collector is 100-1000 g/ton magnesite; the mass ratio of the foaming agent to the amine cationic collector is 4:1.
Still further preferably, the amine cationic collector is dodecylamine.
Still more preferably, the foaming agent is pine oil or/and methyl isobutyl carbinol.
Preferably, the super absorbent resin is one or two of polyacrylate homopolymerization type super absorbent resin and polyacrylic acid-acrylamide copolymerization type super absorbent resin, and the average particle size of the super absorbent resin in a dry state is 120-250 mu m.
Compared with the prior art, the invention has the beneficial effects that: the light-burned magnesium oxide prepared by the invention has the advantages of low hydration water demand, stable hydration product, long expansion duration, adjustable expansion and the like, can improve the volume shrinkage problem of the ultra-high performance concrete, and reduces the shrinkage and cracking risks of the ultra-high performance concrete. The hydration heat absorbent can absorb a large amount of heat in the hydration heat release process of the concrete, so that the temperature rise inside the concrete is not too fast, on one hand, the moisture absorption heat absorbent is favorable for reducing cracks generated due to temperature stress, and on the other hand, the moisture evaporation is favorable for reducing the self-drying phenomenon caused by too low humidity inside the concrete. The super absorbent resin can ensure that the relative humidity in the concrete is moderate, and effectively reduces drying shrinkage and self-shrinkage.
Detailed Description
The technical solution of the present invention is described in detail and fully with reference to the following examples, it is obvious that the described examples are only a part of the examples of the present invention, and not all of the examples. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention. Any equivalent changes or substitutions by those skilled in the art according to the following embodiments are within the scope of the present invention.
Example 1
The embodiment provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which comprises 70 parts of light-burned magnesium oxide, 20 parts of hydration heat absorbent and 10 parts of super absorbent resin; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 120 mu m in a dry state;
the preparation method of the light-burned magnesium oxide comprises the following steps:
crushing magnesite into particles smaller than or equal to 10mm in a two-section one-closed-circuit process consisting of a jaw crusher, a cone crusher and a vibrating screen, grinding by using a ball mill, sieving by using a 200-mesh sieve, entering a flotation process, adding dodecylamine according to the use amount of 500g of magnesite per ton under the natural pH value of ore pulp, adding 2000g of pine oil, stirring for 40min at the speed of 1000rpm, and calcining the obtained concentrate and middling ore for 2h at the temperature of 1100 ℃ to obtain light-burned magnesium oxide through one-rough one-fine reverse flotation; the content of magnesium oxide in the prepared light-burned magnesium oxide is 95 percent, and the residue on the sieve of 0.075mm is not more than 10 percent;
the preparation method of the hydration heat absorbent comprises the following steps:
slowly dripping the prepolymer into the paraffin emulsion, controlling the dripping speed to be 30 drops/min, and controlling the mass ratio of the prepolymer to the paraffin emulsion to be 1:4; after the dripping is finished, heating the obtained mixed solution to 70 ℃ and preserving the heat for 3 hours; after the heat preservation is finished, taking out a sample, sequentially washing the sample for 3 times by using hot water at 60 ℃ and ethanol at 60 ℃, and filtering to obtain the hydration heat absorbent;
the preparation method of the prepolymer comprises the following steps:
uniformly mixing melamine, a 37wt% formaldehyde solution and deionized water according to a mass ratio of 1;
the preparation method of the paraffin emulsion comprises the following steps:
adding styrene-maleic anhydride non-return copolymer powder and sodium hydroxide solid into deionized water, uniformly mixing, heating in a water bath to 90 ℃ and keeping for 1h, adjusting the pH value of the solution to 5 by using citric acid, adding paraffin, emulsifying the paraffin solution at the speed of 16000rpm by using a high-speed dispersion machine after the paraffin is melted, maintaining the emulsifying temperature at 70 ℃, and emulsifying for 4min; the mass ratio of the styrene-maleic anhydride non-return copolymer powder to the sodium hydroxide solid to the deionized water to the paraffin wax is 1.
Example 2
The embodiment provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which comprises 65 parts of light-burned magnesium oxide, 30 parts of hydration heat absorbent and 5 parts of super absorbent resin; the super absorbent resin is polyacrylic acid-acrylamide copolymer super absorbent resin, is white powder, and has an average particle size of 250 μm in a dry state;
the preparation method of the light calcined magnesia is basically the same as that of the embodiment 1, except that the light calcined magnesia is obtained by stirring at the speed of 800rpm for 60min, performing primary coarse-fine reverse flotation, and calcining the obtained concentrate and middling ore at 1150 ℃ for 1h, wherein the content of magnesia in the prepared light calcined magnesia is 95%;
the preparation method of the hydration heat absorbent comprises the following steps:
slowly dripping the prepolymer into the paraffin emulsion, controlling the dripping speed to be 30 drops/min, and controlling the mass ratio of the prepolymer to the paraffin emulsion to be 1:3; after the dripping is finished, heating the obtained mixed solution to 60 ℃ and preserving the heat for 4 hours; after the heat preservation is finished, taking out a sample, sequentially washing the sample for 3 times by using hot water at 60 ℃ and ethanol at 60 ℃, and filtering to obtain the hydration heat absorbent;
the preparation method of the prepolymer comprises the following steps:
uniformly mixing melamine, 40wt% of formaldehyde solution and deionized water according to a mass ratio of 1;
the preparation method of the paraffin emulsion comprises the following steps:
adding styrene-maleic anhydride non-return copolymer powder and sodium hydroxide solid into deionized water, mixing uniformly, heating to 70 ℃ in a water bath, keeping for 2h, adjusting the pH value of the solution to 4 by using tartaric acid, adding paraffin, emulsifying the paraffin solution at 15500rpm by using a high-speed dispersion machine after the paraffin is melted, maintaining the emulsifying temperature at 50 ℃, and emulsifying for 5min; the mass ratio of the styrene-maleic anhydride non-return copolymer powder to the sodium hydroxide solid to the deionized water to the paraffin wax is 1.
Example 3
The embodiment provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which comprises 50 parts of light-burned magnesium oxide, 30 parts of hydration heat absorbent and 20 parts of super absorbent resin; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 180 mu m in a dry state;
the preparation method of the light-burned magnesium oxide is basically the same as that of the embodiment 1, and the difference is that according to the usage amount of 500g of lauryl amine and 2000g of methyl isobutyl carbinol are added into each ton of magnesite, the mixture is stirred for 50min at the speed of 900rpm, and after the rough-fine reverse flotation, the obtained concentrate and middling ore are calcined for 3h at the temperature of 900 ℃ to obtain the light-burned magnesium oxide; the content of magnesium oxide in the prepared light-burned magnesium oxide is 95 percent;
the preparation method of the hydration heat absorbent comprises the following steps:
slowly dripping the prepolymer into the paraffin emulsion, controlling the dripping speed to be 30 drops/min, and controlling the mass ratio of the prepolymer to the paraffin emulsion to be 1:4; after the dripping is finished, heating the obtained mixed solution to 80 ℃ and preserving the heat for 2 hours; after the heat preservation is finished, taking out a sample, sequentially washing the sample for 3 times by using hot water at 60 ℃ and ethanol at 60 ℃, and filtering to obtain the hydration heat absorbent;
the preparation method of the melamine resin solution comprises the following steps:
uniformly mixing melamine, 38wt% of formaldehyde solution and deionized water according to a mass ratio of 1;
the preparation method of the paraffin emulsion comprises the following steps:
adding styrene-maleic anhydride non-return copolymer powder and sodium hydroxide solid into deionized water, uniformly mixing, heating to 80 ℃ in a water bath, keeping for 1.5h, adjusting the pH value of the solution to 5.5 by using tartaric acid, adding paraffin, emulsifying the paraffin solution at a speed of 16500rpm by using a high-speed dispersion machine after the paraffin is melted, and emulsifying for 2min while keeping the emulsifying temperature at 90 ℃; the mass ratio of the styrene-maleic anhydride non-return copolymer powder to the sodium hydroxide solid to the deionized water to the paraffin wax is 1.
Example 4
The embodiment provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which comprises 60 parts of light-burned magnesium oxide, 35 parts of hydration heat absorbent and 5 parts of super absorbent resin; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 200 μm in a dry state; the preparation method of the light-burned magnesium oxide is the same as that of the embodiment 1; the preparation method of the hydration heat absorbent is basically the same as that in example 1, except that the mass ratio of the prepolymer to the paraffin emulsion is 1.
Comparative example 1
The comparative example provides a special shrinkage control anti-cracking agent for ultra-high performance concrete, which comprises 50 parts of light-burned magnesium oxide, 20 parts of hydration heat absorbent and 30 parts of super absorbent resin; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 120 μm in a dry state; the preparation methods of the light burned magnesium oxide and the hydration heat absorbent are the same as example 1.
Comparative example 2
The comparative example provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which comprises 50 parts of light-burned magnesium oxide, 40 parts of hydration heat absorbent and 10 parts of super absorbent resin; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 120 μm in a dry state; the preparation methods of the light burned magnesium oxide and the hydration heat absorbent are the same as example 1.
Comparative example 3
The comparative example provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which comprises 70 parts of light-burned magnesium oxide, 20 parts of hydration heat absorbent and 10 parts of super absorbent resin; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 120 μm in a dry state; the preparation method of the hydration heat absorbent is the same as that of the embodiment 1; the preparation method of the light-burned magnesium oxide comprises the following steps: the magnesite is crushed into particles with the particle size of 10cm, and then the crushed particles are calcined for 3 hours at the temperature of 700 ℃ and 1100 ℃, and mixed and ground into powder with the average particle size of 80 mu m according to the mass ratio of 3:1.
Comparative example 4
The comparative example provides a special shrinkage regulation anti-cracking agent for ultra-high performance concrete, which comprises 70 parts of light-burned magnesia and 30 parts of super absorbent resin; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 120 μm in a dry state; the preparation method of the light-burned magnesium oxide is the same as that of example 1.
Comparative example 5
The comparative example provides a special shrinkage control anti-cracking agent for ultra-high performance concrete, which comprises 70 parts of light-burned magnesia and 30 parts of hydration heat absorbent; the super absorbent resin is sodium polyacrylate super absorbent resin, is white powder, and has an average particle size of 120 μm in a dry state; the preparation method of the lightly calcined magnesium oxide was the same as in example 1.
Performance test
The shrinkage control crack resistance agents prepared in examples 1 to 4 and comparative examples 1 to 5 were added to the ultra-high performance concrete, the mixture ratio is shown in table 1, and the ultra-high performance concrete cement premix in table 1 is the ujinon-UHPC brand ultra-high performance concrete cement premix produced by wuhan-yuan brocade building materials science and technology ltd. The strength of the concrete is tested according to the regulations in GB/T50080-2016 (test method for the performance of common concrete mixtures), the drying shrinkage and the self-shrinkage of the concrete are tested according to GB/T50082-2009 (Standard for test method for the long-term performance and the durability of common concrete), and the performance test results are shown in Table 2.
TABLE 1 ultra high Performance concrete mix proportions
TABLE 2 test results of ultra-high Performance concrete Strength, dry shrinkage and self-shrinkage Properties
As can be seen from Table 2, when the mixing amount of the special shrinkage control crack resistance agent for the ultra-high performance concrete is 10wt% of the glue premix, the 7d drying shrinkage value can be reduced by at least 40.4%, and the 28d drying shrinkage value can be reduced by at least 32.9%. When the super absorbent resin exceeds the limited dosage range or the hydration heat absorbent is used excessively or the preparation method of light burned magnesium oxide is changed or the hydration heat absorbent is lacked or the super absorbent resin is lacked, the prepared anti-cracking agent is added into the super high performance concrete, so that the compression strength and the breaking strength are obviously reduced; particularly, when the hydration heat absorbent or the super absorbent resin is absent in the anti-cracking agent, although the drying shrinkage and the self-shrinkage can be significantly reduced, the flexural strength is reduced by at least 44.9%, and the 28d compressive strength is reduced by at least 29.1%, which seriously affects the performance of the ultra-high performance concrete. This shows that the high water-absorbing resin and the hydration heat absorbent have mutual synergistic effect, and the high water-absorbing resin and the hydration heat absorbent can achieve the best effect when used together in a limited range, thereby not only ensuring the strength of the ultra-high performance concrete, but also achieving excellent anti-cracking effect; the lack of either of them will seriously affect the strength of the ultra-high performance concrete. The light calcined magnesia is doped with magnesia obtained when magnesite is calcined at a lower temperature, so that the activity of the light calcined magnesia is obviously lower than that of the magnesia obtained by calcining at a high temperature in the application.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The present invention may be subject to various modifications and changes by any person skilled in the art. Any simple equivalent changes and modifications made in accordance with the protection scope of the present application and the content of the specification are intended to be included within the protection scope of the present invention.
Claims (9)
1. The special shrinkage regulation anti-cracking agent for the ultra-high performance concrete is characterized by comprising the following raw materials in parts by weight: 50-70 parts of light-burned magnesium oxide; 20-35 parts of a hydration heat absorbent; 5-20 parts of super absorbent resin; the preparation method of the hydration heat absorbent comprises the following steps: slowly dripping the prepolymer into the paraffin emulsion, heating to 60-80 ℃, and reacting for 2-4 h; after the reaction is finished, taking out a sample, washing and filtering to obtain a hydration heat absorbent; the mass ratio of the prepolymer to the paraffin emulsion is 1 (3-4); the preparation method of the prepolymer comprises the following steps:
evenly mixing melamine, formaldehyde solution and deionized water, adjusting the pH value of the solution to 7-9 by using alkali, heating to 50-90 ℃ while stirring, and keeping the temperature for 30-80 min to obtain a prepolymer; the mass fraction of formaldehyde in the formaldehyde solution is 37-40%; the mass ratio of the melamine to the formaldehyde solution to the deionized water is 1 (1-5): (1-10).
2. The special shrinkage regulation anti-cracking agent for the ultra-high performance concrete according to claim 1, wherein the mass ratio of the prepolymer to the paraffin emulsion is 1:4.
3. The special shrinkage-control anti-cracking agent for the ultra-high performance concrete according to claim 1, wherein the mass ratio of the melamine to the formaldehyde solution to the deionized water is 1.
4. The special shrinkage control anti-cracking agent for ultra-high performance concrete according to claim 1, wherein the alkali is triethanolamine.
5. The special shrinkage control anti-cracking agent for the ultra-high performance concrete according to claim 1, wherein the preparation method of the paraffin emulsion comprises the following steps:
mixing styrene-maleic anhydride copolymer, sodium hydroxide and deionized water, heating to 70-90 ℃, keeping the temperature for 1-2 h, adjusting the pH value of the solution to 4-5.5 by using acid, adding paraffin, emulsifying the paraffin solution at 15500-16500 rpm after the paraffin is melted, maintaining the emulsifying temperature at 50-90 ℃, and emulsifying for 2-5min; the mass ratio of the styrene-maleic anhydride non-return copolymer to the sodium hydroxide to the deionized water to the paraffin is 1: (0.15-0.25): (40-50): (10 to 30).
6. The special shrinkage control anti-cracking agent for the ultra-high performance concrete according to claim 5, wherein the mass ratio of the styrene-maleic anhydride non-return copolymer to the sodium hydroxide to the deionized water to the paraffin is 1.
7. The special shrinkage-control anti-cracking agent for ultra-high performance concrete according to claim 5, wherein the acid is citric acid or/and tartaric acid.
8. The special shrinkage control anti-cracking agent for the ultra-high performance concrete according to claim 1, wherein the light-burned magnesia is obtained by crushing, grinding and sieving magnesite as a raw material through a 200-mesh sieve, and then calcining the crushed magnesite at 900-1150 ℃ for 1-3 hours; the content of magnesium oxide in the light-burned magnesium oxide is more than 80 percent, and the screen residue of the light-burned magnesium oxide passing through a 0.075mm sieve is less than or equal to 10 percent.
9. The special shrinkage control anti-cracking agent for ultrahigh-performance concrete according to claim 1, wherein the super absorbent resin is one or two of polyacrylate homopolymerization type super absorbent resin and polyacrylic acid-acrylamide copolymerization type super absorbent resin, and the average particle size of the super absorbent resin in a dry state is 120-250 μm.
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